Deposition apparatus for an organometallic material

ABSTRACT

Means to electrostatically coat a moving substrate includes a liquid source; heated means to vaporize the liquid and to communicate the vapor to a heated, logitudinally slotted dispenser overlying and transversely coextensive with the substrate; and means to establish an electric potential between the slotted dispenser and the substrate whereby to electrostatically effect deposition of the vapor.

[ 51 Dec. 4, 1973 United States Patent 11 1 118/49.5 ll8/49.1 X 119/495X DEPOSITION APPARATUS FOR AN 10/1969 Ing, Jr. et 10/1969 Ehinger et al.ll/l971 ORGANOMETALLIC MATERIAL 75] Inventor:

Burmeister, .lr.

Emery P- M r, Indianapolis, d- 9 1972 Vanderschueren 113/495 [73]Assignee: Ransburg Electro-Coating Corp., 7

12/1966 Gowen.................

2/1972 Krutenat... 6/1960 Walter.......

1 1970 Cariou et al.

Indianapolis, Ind.

July 28, 1972 [22] Filed:

9/1953 Turner.......... ..ll8/5l 7/1954 Appl. No.: 276,113

Related US. Application Data [62] Division of Ser. No. 7,589, Feb. 2,1970, Pat. No.

Primary Examiner-Morris Kaplan Attorney-Merrill N. Johnson et a1.

57 ABSTRACT 323 3 2 Means to electrostatically coat a moving substratein- 1.1 8/491 495 2 cludes a liquid source; heated means to vaporize theC I. n I I] l 5 IL liquid and to communicate the vapor to a heated,

m a a m d M F m 5 1 C N A 3 9 R A 3 N 7, 1 l 9 2 6 2 6 0O 1 1logitudinally slotteddispenser overlying and trans- [56] ReferencesCited versely coextensive with the substrate; and means to UNITED STATESPATENTS establish an electric potential between the slotted dispenserand the substrate whereby to electrostatically In fit 3 h m lea MHB 486556 999 111 HUM l l 225 027 504 929 6 8 2 223 r m 0 P m m n e 2 m f 6 mu.m 1 .H S O W 0 w a XRX 41 9 mM 3 11 This is a division, of application,Ser. No. 007,589,

filed Feb. 2, 1970 and now US. Pat. No. 3,699,027.

The present invention relates to anapparatus for electrostaticallycharging vapors of matter such as an organometallic compound or waterand causing the charged vapors of the matter to be attracted to anddeposited upon a surface of a substrate.

A substrate material such as glass may have one or more of itsproperties such as color, strength, scratchresistance and the likeenhanced by the application thereto of a substance which possesses oneor more properties which aredesiredto be impartedto the substrate. Forexample, it is known that various properties of glass such as color,scratch-resistance and the like can be imparted to glass by depositingupon the glass substances containing oxides of cobalt (Co), chromium(Cr), cerium (Ce), titanium (Ti), zirconium (Zr), aluminum (Al) and thelike. Also, it is known that glass:

substrates having a thin metallic oxide coating firebonded to thesurface thereof can conduct electricity at room temperature whichrenders the substrate advantageous for use in some electricalapplications such as a substrate for integrated circuits.

The deposition of a metallic containing substance or compound upon thesurface of a substrate, such as glass, to improve one or more propertiesof the substrate may be accomplished using several different methods ortechniques. The available methods for depositing the metal containingsubstance or compound upon the substrate include silk screening,electroless deposition, electroplating, cathode sputtering, vacuumevaporation and vapor-phase deposition. Generally, the method selectedto deposit the metal containing substance or-compound upon the substratedepends on a number of factors including the desired uniformity of thedeposit, the thickness of the deposit, the c'omposi tion of the deposit,the availability of the equipment used to deposit the metalliccontaining substance or compound, the composition of the substrate to beworked and the like.

A potential drawback of the silk screen process and of the electrolessprocess is the tendency of the deposit provided by each process toexhibit verylittle, if any, diffusion into the substrate. Without somediffusion of the deposit into the substrate, the bond joint at theinterface between the deposit and the substrate may be tenuous therebyresulting in spalling and the like of the deposit.

The process of electroplating a substrate tends to be influenced byseveral factors including the temperature and the viscosity of theplating bath, the current, agitation of the bath, the concentration ofthe constituents of the bath, the pH of the bath and the like. It isseen that rather strict control of the parameters of the elec-Generally, the vapor-phase deposition method in-' cludes heating andreducing or decomposing a volatile metal halide and depositing the freemetal upon the substrate. The thermally decomposable metal halide iscapable of being divided into its component atoms by dissociation orreduction at a temperature below the melting point temperature of themetallic substance being deposited and below the melting pointtemperatue of the substrate. In addition, the volatile substance shouldbe stable enough to reach the deposition surface before thennaldecomposition takes place. Generally, a suitable gas such as hydrogen ispassed over a liquid metal halide which is heated to a temperaturenecessary to provide the required partial pressure of the metal halidevaponThe gas mixture is passed over the heated substrate in a platingchamber where the metal halide is thermally decomposed to the free metalplus a halogen. The metal deposits on the substrate and the halide maybe recovered by condensation techniques. The process has goodflexibility and is more economical than several of the above-mentionedtechniques; however, the method may not provide uniform deposits unlesshigh gas flow rates are utilized.

The subsequent working or handling of some substrate materials, such aspaper, depends to some extent on the moisture content of the substrate.The properties of paper, for example, for subsequent working and thelike may be enhanced by depositing vapors of water upon the surface of asubstrate material such as paper.

Generally speaking, the present invention relates to a vapor-phase typedeposition method which overcomes several of the problems discussedabove. More particularly, the method includes the step of vaporizingmatter such as water or a suitable organometallic compound of Al, Ti orZr and transporting the vaporized matter' with a suitable gaseouscarrier to an electrostatic charging device. The electrostatic chargingdetroplating process may be required to achieve the desired deposit upona substrate.

One of the drawbacks of cathode sputtering is that l the processrequires from minutes-to hours to deposit 1 a film upon the substratewhereas other techniques require seconds to minutes to deposit a film ofcomparable thickness upon the substrate. The vacuum evaporation processrequires elaborate equipment to establish the necessary vacuumevaporation environment. In addition, neither cathode sputtering norvacuum evaporation readily lend themselves to' automated techniques.

vice electrically charges the vapor of the matter. The

charged vapor of the matter is directed toward, at-.

tracted'to and deposited upon a surface of the substrate. Where thevapor is an organometallic compound, the deposited organometalliccompound is caused to decompose'and produce a metal containingdepositupon the surface of substrate upon which it is deposited. After thedeposition of the vapors or in the case of organometallic compounds,decomposition of the organometallic compound vapors on the surface ofthe substrate, other substances may be applied, as desired, to thetreated surface of the substrate. The other substances may be lubricantsand the like.

It is, therefore, an object of the present invention to provide anapparatus for electrostatically charging and depositing charged vaporsof matter upon asurface of FIG. 2 is a side view of a means forproducing the organometallic compound vapors;

It is to be understood that the apparatus of the present invention isapplicable to the deposition of vapors of matter other than vapors of anorganometallic compound to a substrate other than glass. For example,the apparatus and the method may be used to deposit water vapor than asubstrate such as paper. However, for the purpose of illustration andnot for the purpose of limitation, the invention will be described usingvapors of an organometallic compound as an example of a vapor of aspecific matter and using glass as an example of a specific substratematerial.

Referring now to FIG. 1 of the drawing, an apparatus for producing andelectrostatically charging vapors of an organometallic compound anddepositing such vapors upon a substrate is indicated by referencenumeral 11. The apparatus 11 includes means 12 for vaporizing anorganometallic compound 13 and an electrostatic means 14, connected tovaporizing means 12 by a suitable conduit 15, for suitably distributingand electrostatically charging the vaporized organometallic compound.

The means 14 for electrostatically charging the vapors of theorganometallic compound includes an elongated member 16in spaced,substantially parallel relationship with surface 17 of the substrate 10upon which the electrostatically charged vapors are to be deposited. Themember 16 is preferably fabricated from a suitable, electricallyconductive material that is substantially chemically inert with respectto the vapors of the organometallic compound. A support means 18,

fabricated from a suitable electrically insulative mate rial, is used todeterminately space member 16 from surface 17 of the substrate.

The member 16 is suitably connected to the ungrounded terminal of directcurrent (DC) power supply 19. DC. power supply 19 is capable ofproviding member 16 with a direct current voltage of up to 100,000 voltsor higher. The member 16 presents to the surface 17 of the substrate 10a relatively sharp or attenuated edge 20. An average potential gradientof about 8,000 volts per inch or higher, preferably about 20,000 voltsper inch or higher, is maintained between the relatively sharp orattenuated edge 20 of the mem-' ber 16 and the substrate 10. Forexample, if the attenuated edge 20 of member 16 is spaced 5 inches fromsurface 17 of the substrate 10 and the direct current source 19 provides100,000 volts to the attenuated edge and the surface- 17 is grounded,the average potential gradient between the edge 20 and the surface 17 ofthe substrate is about 20,000 volts per inch.

The substrate 17 is connected to ground by any suitable means. Thegrounding of the substrate 10 provides the substrate with anelectrostatic spray attracting potential.

Since, during the operation of the apparatus 14, an

average potential gradient of about 8,000 volts per inch in depositingthe charged vapors of the organometallic compound upon the surface 17 ina substantially uniform manner.

Vapors of the organometallic compound 13 are conveyed to the attenuatededge 20 of member 16 via conduit 15. The conduit 15 is fabricated fromany suitable material which is chemically inert to'the vapors of theorganometallic compound 13 and which is substantially uneffected by theelevated temperature of the organometallic compound. A suitableresistanceheating means 33 is connected to the conduit 15 to maintainthe temperature within the conduit above a predetermined temperature.Resistance heating means 33 is energized by power supply 34. Theresistance heating means 33 iselectrically isolated from the potentialor voltage of DC. power supply 19.

A suitable resistance heating means 28 is located within the member 16to maintain the temperature of the vapors of the organometallic material13 above the boiling point temperature of the material. The resistanceheating means 28 is connected to a suitable power supply 22. Theresistance heating means 28 is electrically isolated from the potentialor voltage of DC. power supply 19.

The organometallic compound to be vaporized and electrostaticallydeposited upon surface 17 of the substrate' 10 should have a boilingpoint or vaporization temperature somewhat below its decompositiontemperature. For simplicity in the treatment of the surface of thesubstrate by the organometallic compound, the decomposition temperatureof the vapors of the organometallic compound should be somewhat lessthan the melting point temperature of the substrate or in the case of aglass substrate, the decomposition temperature of the vapors of theorganometallic compound should not exceed the softening pointtemperature of the glass. The softening point temperature of severalcommercially available glasses is'about 500C to about 1,500c.

It is to be understood that the expression softening point temperatureis the temperature or range of temperatures at which a particular glasssoftens prior to melting.

An organometallic compound whose vapors decompose upon or after contactwith a heated surface in the temperature range of about 350C to about600C to produce a metal oxide having a melting point temperature higherthan the melting point temperature of the substrate is applicable to thepresent invention. However, it is to be understood that the compoundshould not undergo significant decomposition prior to contact with theheated surface of the substrate. Furthermore, a preferred metalcontaining deposit upon a glass substrate has a thermal coefficient ofexpansion similar to that of the glass to reduce the possibility ofseparation on cooling or temperature cycling of the substrate.

Volatile organometallic compounds of Al, Ti, Zr and the like whichproduce oxides of Al, Ti, and Zr, having melting point temperatures inexcess of about l,500C, are satisfactory for the intended purpose of theinstant invention. Examples of suitable organometallic compounds ofaluminum are aluminum ethoxide and aluminum isopropoxide with aluminumisopropoxide being preferred. Aluminum isopropoxide vaporizes at atemperature of about C. A suitable example of an organometallic compoundof zirconium is tetra-t-butyl zirconate which vaporizes at a temperatureof about C. A suitable example of an' organometallic com- 0.1 mm. Hg isdesirable. Concentrations corresponding to partial pressures of about0;1-. to 50mm. Hg are preferred. Higher concentrations, e .g., u p to l00% can be used. The vapors can be diluted and transported to theelectrostatic charging means by any carrier gas which does notchemically react with or cause decomposition of the vaporizedorganometallic compound. Suitable carrier gasesare nitrogen, argon,methane, air and the like. Of the several named carrier gases, air ispreferred since air functions as well as, for example, nitrogen and isreadily available.

The carrier gas should'be heated to a-temperature which exceeds theboiling point or vaporization temperature of the organometallic compoundto substantially prevent premature condensation of the organometalliccompound. The temperature of the carrier gas should be less than thetemperature required to decompose the organometallic compound to therebysubstantially prevent decomposition prior. to deposition upon asubstrate.

The organometallic compound vapors of Al, Ti, and Zr, and in particlarorganometallic compound vapors of Ti, tend to hydrolyze upon contactwithwater or water vapor. Therefore, water vapor or moisture should beexcluded from the carrier gas. It is seen that deposition of the vaporsof the organometallic compound is facilitated by using an environmentwhich excludes as much water vapor or moisture as is practicallypossible.

The surface 17 of substrate 10 may be any materialwhich is able to beraised to a temperature which will cause the deposited vapors of theorganometallic compound to react therewith to produce metaloxide-containing deposit thereon. The substrate maybe a laminated bodyas long as the bond at the inface between adjacent laminae is notharmfully effected upon cooling of the laminated substrate from theelevated temperature.

- One suitable substrate material is glass which can be heated to atemperature of about 350C to about 600C preferably about 450C to about600C without experiencing' harmful deformation. A suitable glass whichmay be used as a substrate are soda-lime or lime glass that includeabout 20 weight percent sodium oxide (Na O), about 5 weight percentcalcium oxide (CaO), about 70 to about 75 weight percent silica'(SiO andsmall amounts of other compounds. Other suitableglasses which may be.used as a substrate are silicate glass, silica glass, bore-silicateglass which includes up toabout 5 weight percent boric oxide (B 0aluminosilicate glass, alabaster, solder glass, soda-zinc glass,potash-soda-lead glass, 96 weight percent silica glass and the like.Glass having a softening point temperature in the range of about 600C toabout 800C is preferred for more advantageous bonding of the metalcontaining material appears to occur. Several glasses which have asoftening point temperature between 600C and 800C are soda-lime (700C),potash-soda lead (625C), borosilicate (750C780C) and alabaster (670C).

The substrate may'be heated to a temperature of about 350C or highersubsequent to the deposition of the electrostatically charged vapors ofthe organometallic compound thereon or, alternatively, the substrate maybe heated to a temperature of about 350C or higher prior to thedeposition of the vapors of the organometallic compound thereon so thatdecomposition of the compound is initiated as the compound contacts thesurface of the substrate. For example, glass produced by thePilkington'et a1 process described in'U.S. Pat. No. 2,91 1,759 may besubjected to electrostatic deposition of the vapors of theorganometallic compound while the glass is in the temperature range of350C to 600C but prior to an initial cooling to a tem' perature belowabout 350C. v

Referring'again to FIG. 1 of the drawing, an organometallic compound 13from source reservoir 24 is introduced in droplet fashion into asuitable device such as tubular column 21 through inlet port 23. Theinterior; of'column 21 is maintained at a temperature above the boilingpoint or vaporization temperature of the or ganometallic compound by'asuitable resistance heating means 22 positioned exteriorly of the column21. The heating means 22 is suitably energized by power supply 35.

A suitable source 36 of a preheated carrier gas is used to provide astream of substantially moisture free carrier gas such as air-.to thecolumn 2l through inlet port 25 formed in the bottom of the column. Thesubstantially moisture free carrier gas is preheated to a temperatureabove the boiling point temperature of the organometallic compound butbelow the decomposition temperature of the compound. The carrier gasmixes with the vapors of the organometallic compound providing avapor-gas mixture. The organometallic compound vapor-gas mixture passesfrom the column 21 through the outlet port 26 to preheated conduit 15.The conduit 15 is heated to a temperature sufficient to substantiallyprevent condensation or decomposition of the vapor ofth'e organometalliccompound.

The organometallic compound vapor-gas mixture-is emitted along edge 20of member 16. The voltage maintained on device 14 produces a highelectrical potential gradient at edge 20 thereof. The high electricalpotential gradient creates an abundance of gas-ions. The gas ions,because they tend to be drawn toward the surface 17, bombard and chargethe vapor particles emerging through the slot at edge 20. The vapor,-therefore, is electrostatically charged by the electrostatic device 14.The electrostatically charged vapors of the organometallic compound'aredeposited upon the surface l7-of substrate 10.

The surface 17 of the substrate 10 may be heated to atemperature ofabout 350C to about 600C, alternatively, surface 17 subsequently may beheated to about 350C to about 600C to cause decomposition of the'organometallic compound thereby producing a metal containing deposit onsurface 17 of the substrate 10.

A suitable environmental chamber 27 circumscribes a conveyor (not shown)used to transport the substrate 10 beneath the electrostatic device 14.The chamber 27 reduces air drafts and excludes as much water vapor ormoisture as is possible fromthe area where the vapors of theorganometallic compound are deposited and decomposed upon thesubstrate.

Subsequent to the decomposition of the organometallic compound toproduce a metal containing deposit upon surface 17 of the substrate,other suitable compositions may be applied to the surface 17. Forexample, substrate of ammonium and pilyoxyethylene, bees wax,hydrogenated animal oil and the like may be applied to surface 17 toassist in providing surface 17 with a more advantageous property orproperties.

FIG/2 shows yet another method which may be used to provide anorganometallic compound-vapor-gas mixture. The organometallic vaporstream is produced by bubbling a suitable carrier gas through a'liquid30 of the organometallic compound contained within reser- 'voir 31. Theliquid 30 of the organometallic compound is heated to a temperatureabove the vaporization temperature by suitable heat source 32. Thecarrier gas transports the organometallic compound vapors from reservoir31 to the electrostatic charging device 14.

It is to be understood that mixtures of the vapors of severalorganometallic compounds are contemplated to be deposited using themethod of the'present invention.

The following examples are illustrative of the method for depositingelectrostatically charged vapors ofan organometallic compound upon asurface of a substrate.

EXAMPLE 1 Glass heated to a temperature of about 550C 'is transported tochamber 27 A gaseous stream of preheated nitrogen and tetraisopropyltitanate is prepared using the apparatus of FIG. 1 by substantiallysaturating a stream of preheated nitrogen with tetraisopropyl titanatevapors. The tetraisopropyl titanate is vaporized at about 75C. Themixture of tetraisopropyl titanate and nitrogen is diluted with about 8volumes of 1 of additional nitrogen. The stream of nitrogen andtetraisopropyl titanate vapors is fed to the electrostatic device usingthe apparatus of FIG. 1. The edge of the electrost atic device is placedabout 8 inches above the I grounded surface of the glass and chargedwith a DC EXAMPLE 2 The procedure of EXAMPLE I is followed duringaluminum isopropoxide vaporized at 90C. In this example thenitrogen-aluminum isopropoxide mixture is diluted with 19 volumes to lof additional nitrogen.

The glass includes a deposit of an oxide of aluminum.

the organometallic compound tetra-t-butyl zirconate' vaporized at C. Thenitrogen-t-butyl zirconate mixture is diluted to one twentieth withadditional nitrogen. The glass has a deposit of an oxide of zirconium.

EXAMPLE 4 EXAMPLE 5 The procedure of EXAMPLE I is followed except thatthe temperature of the glass, when contacted with thenitrogen-tetraisopropyl titanate mixture is 350C.

The glass causes decomposition of the organometallic,

compound when heated subsequently to 550C to thereby produce a depositof an oxide of titanium.

The thickness of the metal oxide deposit upon the surface of thesubstrate depends upon, among other things, the length of time thesurface of the substrate is subjected to the vapors of theorganometallic compound, the vapor concentration of the organometalliccompound in the carrier gas and the like. Therefore, contact times froma few seconds to 20 time or more may be necessary to obtain the desiredthickness of the metal oxide containing deposit. Where a contact tim ofa minute or more is contemplated, the chamber 27 may be enlarged toaccommodate more than one electrostatic charging device 14. A depositthickness in the range of about 0.005 to about 2 or more microns iscontemplated by the present invention with a deposit thickness in therange of about 0.01 to about 1 micron being preferred. I

It should be understood that the heating means 22, the power supply 34,the power supply 35, the resis tance heating means 28, the resistanceheating means 33, the resistance heating means 22 and any otherelectrical means associated 'with the apparatus 11 are electricallyisolated from the potential or voltage of DC. power supply l9.'Also, itshould be understood that column 21, reservoir 24 and source 36 areisolated from ground potential.

I claim: 1. An apparatus for depositing an organometallic material on asubstrate comprising a source of organometallic material, means to forma vapor of the organometallic material including a member providing achamber with a heater capable of maintaining the temperature within themember suflicient to vaporize the organometallic material but below thetemperature at which it decomposes, and means to introducetheorganometallic material into the member in droplet fashion; means toelectrostatically charge the organometallic vapor and to provide adepositing electrostatic field to the substrate including an elongatedslotted member supported spaced from but parallel to the substrate to becoated and having an attenuated edge adjacent the slot and carrying aresistance heater electrically isolated from the member, said elongatedslotted member being connected with a direct current power supply tocharge the member to high voltage with respect to the substrate;

a heated conduit from the vaporizing means to the electrostaticdepositing means;

an environment chamber substantially enclosing the electrostaticdepositing means and the substrate adjacent thereto; and

means to supply a flow of dry preheated carrier gas to the vaporizingmeans to provide a continuous flow of vapor through the conduit to theslot of the electrostatic depositing means for continuous charging anddeposition on the substrate.

* II! t i

